The invention relates to a multi-disk clutch in a power split transmission for driving a mobile vehicle, especially a field tractor. The installation space, particularly the radial extent of the transmission, is limited wherefore the transmission housing must not exceed a maximum extension. The multi-disk clutch of the transmission is used to reverse the vehicle direction, it being possible for the operation to develop automatedly. At the same time, the clutch must be designed in a manner such that the closing force of the shift piston of the multi-disk clutch is independent of the rotational speed and a calibration of the clutch is possible. When the clutch is open, the drag losses of the disks must be kept at a low level, since in a multi-disk clutch used as reversing clutch, when a clutch is in open state the disks always have to be driven through in counter engine rotation.
DE 195 22 833 has disclosed a power split transmission where two multi-disk clutches connected downstream of the power split part of the transmission are disposed in a manner such that by closing the first clutch KV and opening the second clutch KR, the vehicle is moved forward by closing the second clutch and opening the first clutch, the vehicle is moved in reverse. By arrangement of the clutches radially next to each other, a larger radial installation space is needed.
DE 34 32 403 has disclosed a multi-disk clutch designed as double clutch in which rotational-speed dependent hydraulic axial forces on the shift piston counteract the rotational-speed dependent hydraulic axial forces on a radially inwardly open compensating cylinder having a chamber filled to over flow with cooling oil. The oil fed to the compensating piston is also passed on to the compensating cylinder and via the disks escapes into the transmission. When the clutch is open, especially at low temperatures and due to the drag losses generated thereby in the multi-disk clutch, the degree of efficiency is also impaired.
The problem on which the invention is based is to provide a double clutch for a power spit transmission which stands out by a compact design, low number of parts, an improved degree of efficiency, the same as by the prevention of wobbling disks and the property of being automatedly shiftable.
According to the invention, this is achieved by the fact that the clutch used is a multi-disk clutch designed according to the double clutch principle, which is connected downstream of the power split part of the transmission and where both individual clutches rotate in opposite directions, which is obtained by using one countershaft connected downstream of the clutch driven in reverse. By said arrangement of the multi-disk clutch, a compact, space-saving solution is achieved. By this arrangement, the clutch can be used as reversing clutch to reverse the vehicle direction, as separating clutch by opening both disk set, as parking brake, as starting clutch and as brake for dynamic brake support by closing both disk sets. By using the double clutch as reversing clutch with separate clutches rotating in different directions, it is possible to construct the clutches so that when the clutches are open the drag torques produced by the disk sets compensate each other and thus no starting torque is produced upon the vehicle. It is further possible to mount all supplies and discharges in the central shaft which can also be used as torque-transmitting duct for other possible inputs, particularly the fluid for the volume of the compensating piston for compensation of the rotational-speed dependent axial forces can be delivered and discharged through the central shaft. By the fluid for the volume of the compensating piston for compensation of the rotational-speed dependent axial forces being returned through the central shaft, the degree of efficiency is improved in a manner such that the drained fluid is not passed through the disks and the drag torques and losses associated therewith are reduced. The connecting holes toward the shift piston, the same as to the compensating piston, are located radially at the same height thus ensuring that the rotational forces are exactly compensated. By surfaces of the same size on both sides of the shift piston being covered with fluid, the rotational-speed dependent axial forces reciprocally cancel each other. Due to the rotational-speed dependent axial forces on both sides of the shift piston, no additional drain valves are needed for the pressurized space of the shift piston. In addition, a valve can be provided in the clutch device which releases a fluid current for cooling the disks of the clutch only when the clutch becomes closed or is closed. In the open state, the valve closes the access for the fluid current to the disks which further reduces the drag torques thus improving the degree of efficiency. In order to automate the gear shift of the clutch, it is necessary that the clutch be calibrated for which purpose it must be possible to detect the point at which the disks touch each other but still transmit no torque. Therefore, in the invention is used a spring characteristic line which is composed of the spring tension for the resetting of the disks in such a manner that the characteristic line is always increasing. It is thus possible to coordinate with the control of the clutch a specific path of the piston for each clutch pressure or spring tension.
In order further to reduce the drag torque of the disks, it is necessary to keep the disks at a defined distance.
In this invention, therefore, the outer disks are easily kept by corrugated springs at a defined distance between the outer disks. By using corrugated springs, it is ensured that a wobbling of the disks be prevented which prevents as inadmissible heating of the disks.